//modbus PDU 结构体
typedef struct tagModbusPDU
{
    uint8_t u8Func;
    uint8_t *pu8Data; //指向databuff的指针
    uint8_t u8DataLen; //数据域长度
}MbPDU_t;

//modbus ADU 结构体
typedef struct tagMdobusADU
{
    uint8_t  u8Addr;
    MbPDU_t  Pdu;
    uint16_t u16CRC; //MB CRC16 Lo在高位，Hi在低位
}MbADU_t;

/*******************************************************************************
*反转CRC16ModBus表，实际MSB为低8位，LSB为高8位。为配合正序CRC16算法，高低位互换
*ModBus数据流中：
*
*Data[n],              Data[n-1],            Data[n-2],...,Data[1],Data[0]
*CRC16Hi(CRCtableLSB), CRC16Lo(CRCtableMSB),...
*
*从Data[0]开始读取先读低位至Data[n]。
*按正序字节型CRC16算法，相当于Data[n-1]为高8位，Data[n]为低8位。
*******************************************************************************/
const uint8_t CRCtableMSB[]=
{
	0x00,0xc1,0x81,0x40,0x01,0xc0,0x80,0x41,0x01,0xc0,
	0x80,0x41,0x00,0xc1,0x81,0x40,0x01,0xc0,0x80,0x41,
	0x00,0xc1,0x81,0x40,0x00,0xc1,0x81,0x40,0x01,0xc0,
	0x80,0x41,0x01,0xc0,0x80,0x41,0x00,0xc1,0x81,0x40,
	0x00,0xc1,0x81,0x40,0x01,0xc0,0x80,0x41,0x00,0xc1,
	0x81,0x40,0x01,0xc0,0x80,0x41,0x01,0xc0,0x80,0x41,
	0x00,0xc1,0x81,0x40,0x01,0xc0,0x80,0x41,0x00,0xc1,
	0x81,0x40,0x00,0xc1,0x81,0x40,0x01,0xc0,0x80,0x41,
	0x00,0xc1,0x81,0x40,0x01,0xc0,0x80,0x41,0x01,0xc0,
	0x80,0x41,0x00,0xc1,0x81,0x40,0x00,0xc1,0x81,0x40,
	0x01,0xc0,0x80,0x41,0x01,0xc0,0x80,0x41,0x00,0xc1,
	0x81,0x40,0x01,0xc0,0x80,0x41,0x00,0xc1,0x81,0x40,
	0x00,0xc1,0x81,0x40,0x01,0xc0,0x80,0x41,0x01,0xc0,
	0x80,0x41,0x00,0xc1,0x81,0x40,0x00,0xc1,0x81,0x40,
	0x01,0xc0,0x80,0x41,0x00,0xc1,0x81,0x40,0x01,0xc0,
	0x80,0x41,0x01,0xc0,0x80,0x41,0x00,0xc1,0x81,0x40,
	0x00,0xc1,0x81,0x40,0x01,0xc0,0x80,0x41,0x01,0xc0,
	0x80,0x41,0x00,0xc1,0x81,0x40,0x01,0xc0,0x80,0x41,
	0x00,0xc1,0x81,0x40,0x00,0xc1,0x81,0x40,0x01,0xc0,
	0x80,0x41,0x00,0xc1,0x81,0x40,0x01,0xc0,0x80,0x41,
	0x01,0xc0,0x80,0x41,0x00,0xc1,0x81,0x40,0x01,0xc0,
	0x80,0x41,0x00,0xc1,0x81,0x40,0x00,0xc1,0x81,0x40,
	0x01,0xc0,0x80,0x41,0x01,0xc0,0x80,0x41,0x00,0xc1,
	0x81,0x40,0x00,0xc1,0x81,0x40,0x01,0xc0,0x80,0x41,
	0x00,0xc1,0x81,0x40,0x01,0xc0,0x80,0x41,0x01,0xc0,
	0x80,0x41,0x00,0xc1,0x81,0x40
};

const uint8_t CRCtableLSB[]=
{
	0x00,0xc0,0xc1,0x01,0xc3,0x03,0x02,0xc2,0xc6,0x06,
	0x07,0xc7,0x05,0xc5,0xc4,0x04,0xcc,0x0c,0x0d,0xcd,
	0x0f,0xcf,0xce,0x0e,0x0a,0xca,0xcb,0x0b,0xc9,0x09,
	0x08,0xc8,0xd8,0x18,0x19,0xd9,0x1b,0xdb,0xda,0x1a,
	0x1e,0xde,0xdf,0x1f,0xdd,0x1d,0x1c,0xdc,0x14,0xd4,
	0xd5,0x15,0xd7,0x17,0x16,0xd6,0xd2,0x12,0x13,0xd3,
	0x11,0xd1,0xd0,0x10,0xf0,0x30,0x31,0xf1,0x33,0xf3,
	0xf2,0x32,0x36,0xf6,0xf7,0x37,0xf5,0x35,0x34,0xf4,
	0x3c,0xfc,0xfd,0x3d,0xff,0x3f,0x3e,0xfe,0xfa,0x3a,
	0x3b,0xfb,0x39,0xf9,0xf8,0x38,0x28,0xe8,0xe9,0x29,
	0xeb,0x2b,0x2a,0xea,0xee,0x2e,0x2f,0xef,0x2d,0xed,
	0xec,0x2c,0xe4,0x24,0x25,0xe5,0x27,0xe7,0xe6,0x26,
	0x22,0xe2,0xe3,0x23,0xe1,0x21,0x20,0xe0,0xa0,0x60,
	0x61,0xa1,0x63,0xa3,0xa2,0x62,0x66,0xa6,0xa7,0x67,
	0xa5,0x65,0x64,0xa4,0x6c,0xac,0xad,0x6d,0xaf,0x6f,
	0x6e,0xae,0xaa,0x6a,0x6b,0xab,0x69,0xa9,0xa8,0x68,
	0x78,0xb8,0xb9,0x79,0xbb,0x7b,0x7a,0xba,0xbe,0x7e,
	0x7f,0xbf,0x7d,0xbd,0xbc,0x7c,0xb4,0x74,0x75,0xb5,
	0x77,0xb7,0xb6,0x76,0x72,0xb2,0xb3,0x73,0xb1,0x71,
	0x70,0xb0,0x50,0x90,0x91,0x51,0x93,0x53,0x52,0x92,
	0x96,0x56,0x57,0x97,0x55,0x95,0x94,0x54,0x9c,0x5c,
	0x5d,0x9d,0x5f,0x9f,0x9e,0x5e,0x5a,0x9a,0x9b,0x5b,
	0x99,0x59,0x58,0x98,0x88,0x48,0x49,0x89,0x4b,0x8b,
	0x8a,0x4a,0x4e,0x8e,0x8f,0x4f,0x8d,0x4d,0x4c,0x8c,
	0x44,0x84,0x85,0x45,0x87,0x47,0x46,0x86,0x82,0x42,
	0x43,0x83,0x41,0x81,0x80,0x40
};

/********************************************************************************
*函数功能: Modbus CRC 校验，字节型算法，返回mosbus CRC16高低互换
*修改记录:
*日期:                作者:                摘要:
      20-04-27             YummoShin            Create
********************************************************************************/
static uint16_t u16CrcCal(MbADU_t *pADU)
{
    uint8_t i = 0, idx = 0;
    uint8_t CrcHi = 0xFF;		//CRC初值，字节型算法名义上的高位
    uint8_t CrcLo = 0xFF;		//CRC初值，字节型算法名义上的低位
    uint16_t CRC16;

    //地址字节
    idx = CrcHi^(pADU->u8Addr);
    CrcHi = CrcLo^(CRCtableMSB[idx]);
    CrcLo = CRCtableLSB[idx];
    //功能码
    idx = CrcHi^(pADU->Pdu.u8Func);
    CrcHi = CrcLo^(CRCtableMSB[idx]);
    CrcLo = CRCtableLSB[idx];
    //PDU域中Data
    for(i=0; i<(pADU->Pdu.u8DataLen); i++)
    {
        idx = CrcHi^((pADU->Pdu.pu8Data)[i]);
        CrcHi = CrcLo^(CRCtableMSB[idx]);
        CrcLo = CRCtableLSB[idx];
    }
	//因为CRC table 是高低位互换的，
	//故CrcHi对应ModbusCRC16低位，CrcLo对应ModbusCRC16高位
	//返回对应modbusRTU格式的CRC16低位在前、高位在后
    CRC16 = (CrcHi<<8)+CrcLo; 

    return CRC16;
}
